1. Field of the Invention
The present invention relates to method and apparatus for performing perforating operations, and, more particularly, to performing wireless perforating gun operations.
2. Description of the Prior Art
For purposes of enhancing production from a subterranean formation, a perforating gun typically is lowered down into a wellbore that extends through the formation. A perforating gun comprises a plurality of radially-oriented shaped charges which are detonated to penetrate and form perforations through the casing and cement into the formation proximate the wellbore. The shaped charges typically are distributed at points along a helical spiral that extends around the longitudinal axis of the perforating gun.
In wireline guns, there are normally two wires that run the length of the gun string. One of these wires is a live or hot wire which is connected to a positive or negative voltage, and the other wire is a ground wire. These wires are needed to connect a source of current and voltage which is located at or near the earth's surface to the electrical detonator in the body of the perforating gun. The electrical detonator is the apparatus that initiates the ballistic train including the detonating cord and subsequently the shaped charges which will perforate the well and permit flow between the reservoir in the formation and the wellbore. In some cases, the gun body has been used as the ground wire.
It frequently occurs that the live wire gets pinched during loading or transportation or even after arming of the perforating gun. The live wire may become an open circuit as a result of being pinched or may be shorted to ground which results in the hot wire no longer maintaining isolation from the ground. In either event, current and voltage never reach the detonator.
The presence of the wires decreases the amount of space in the gun for shaped charges and hence decreases the size of shaped charges which may be employed. The presence of the wires also increases the amount of time required to load a gun, and if a cable gets pinched or shorts out during the loading or transporting process, the wires must be replaced and reinstalled in the gun, which increases the time necessary for loading. The problems with the wires that are used in activating the electrical detonators are believed to contribute significantly to quality issues with respect to wireline perforating services.